The invention relates to an apparatus and a method for carrying out chemical and physical materials transformations.
Apparatuses such as ball mills or stirred ball mills are available for producing fine dispersions. A disadvantage of these apparatuses is the abrasion of the milling media used, for example milling media composed of glass, ceramic, metal or sand. This abraded material restricts the use of the dispersions produced in this way in fields which tolerate only a low level of impurities, for example the polishing of sensitive surfaces.
Higher energy inputs are possible using a planetary kneader/mixer. However, the effectiveness of this system relies on a sufficiently high viscosity of the mixture being processed in order to introduce the necessary high shear energies for breaking up the particles.
Although very fine dispersions can be produced using high-pressure homogenizers in which a predispersion which is under high pressure impinges on armoured wall regions of a chamber, it has been found that the chamber of such an apparatus is subject to severe wear despite the armouring. Division of the predispersion into two streams which are depressurized via a nozzle and impinge precisely on one another reduces the abrasion but does not solve the problem. Centring of the predispersions directed at one another is especially difficult. Such a method is described, for example, in EP-A-766997.
EP-B-1165224 describes a method in which the abrasion in the production of dispersions is significantly reduced when the divided predispersion streams which are under high pressure are depressurized to a common collision point which is located in a gas-filled milling space far from material. This arrangement is said to minimize cavitation on walls of materials, in contrast to the abovementioned high-pressure apparatuses which operate in a liquid-filled milling space. The gas stream here also takes on the task of transporting the dispersion from the milling space and cooling the dispersion. A disadvantage of this method is the work-up of the gas/dispersion mixtures. To achieve economically viable throughputs, large amounts of gas have to be used. The separation of this gas from the dispersion requires an increased outlay in terms of apparatus, for example appropriately dimensioned degasers. The reduced thermal conductivity resulting from the high proportion of gas requires larger and thus more expensive cooling facilities in the event of cooling of the mixture being required.
DE-C-10204470 describes the use of steam as gas. Here too, the collision of the particles to be dispersed takes place in a space far from materials. The use of steam enables the disadvantages of the method of EP-B-1165224 in which large amounts of gas have to be removed from the reaction mixture to be avoided. Nevertheless, even in the method of DE-C-10204470, it is found that maintenance of a gas atmosphere during dispersion is not economically viable.
DE-A-10360766 describes a method in which the milling space is flooded with a predispersion, as a result of which the work-up of mixtures of gas and dispersion can be avoided.
DE-A-10141054 describes a reactor in which, after alignment of the fluid jets, rotatably supported hard bodies, for example ceramic spheres, are additionally introduced into the path of the jet. This leads to the fluid jets not impinging on the reactor wall in the event of alignment being lost and thus leading to destruction of the entire reactor, but merely impinging on the replaceable ceramic spheres. However, it has been found that the effect of such an apparatus is only short-term since the movement of the rotatably supported hard bodies likewise results in abrasion at places in the reactor where the hard bodies are positioned and contact the wall. As a consequence, the loss of alignment of the fluid jets caused thereby leads to further damage to the reactor.
All the apparatuses mentioned in which physical or chemical materials transformations are carried out under high pressure have the disadvantage that abrasion of material occurs under the extreme conditions. This firstly contaminates the reaction product and, secondly, such a reactor cannot be operated economically.